1. Technical Field
The present invention relates to a variable capacitance type capacitor that detects externally applied pressure as a change in capacitance.
2. Background Art
As an example of a position input device used as an input device for a personal computer or the like, there is known for example a position input device including a position indicator, the position indicator having the shape of a pen and including a pen pressure detecting section, and a position detecting device having an input surface on which a pointing operation and the input of characters, figures, and the like are performed by using the position indicator.
A variable capacitance type capacitor as described in Patent Document 1 (Japanese Patent Laid-Open No. Hei 04-96212) has conventionally been used as the pen pressure detecting section of the position indicator. The variable capacitance type capacitor described in this Patent Document 1 includes, as mechanistic structural parts housed within a long and thin cylindrical casing, a first conductor attached to one end surface of a cylindrical dielectric and a flexible second conductor capable of elastic displacement disposed on another end surface side of the dielectric opposite to the one end surface of the dielectric. A surface of the second conductor, which faces the dielectric, has such a shape as to swell in the form of a dome toward the dielectric, for example.
The variable capacitance type capacitor described in Patent Document 1 also includes a spacer for separating the second conductor from the other end surface of the dielectric by a small interval except for a portion of the second conductor and the other end surface of the dielectric. The variable capacitance type capacitor also includes a part for applying a relative pressure or displacement between the second conductor and the dielectric. The part for applying the relative pressure or displacement is coupled to a core body of the pen-shaped position indicator. When a pen pressure is applied to the position indicator from one end part of the casing of the position indicator, a force applied in an axial direction to the core body displaces the flexible second conductor toward the dielectric side, and thus causes the second conductor to touch the other end surface of the dielectric. Then, the swelling end surface of the flexible second conductor is in the shape of a dome touches the other end surface of the dielectric with a contact area corresponding to the pressing force. Therefore a capacitance formed between the second conductor and the first conductor with the dielectric interposed therebetween changes.